But on a privious Version, at least on my Site /?flush=1 was much faster.
And did did not lead to Timeout.
Just testet on a Page with not much Content: 4:20min!!
Before it was something less one minute.

From my experience it takes ages on my local windows machine with wamp, and it takes much less on the production lunix server - but past that the time it takes is the time it takes. I have the execution time high on my local machine.

is said: "We recommend using a PHP accelerator or opcode cache, such as xcache or WinCache."
It is APC installed on the Server (can it has something to do with it? Should I use xcache? I've read somewere else that others using APC too with Silverstripe)

Edit 4: Because it's sometimes very fast and sometimes extremly slow. I think there is maybe not enough CPU Power on the Server.

What machine are you running? FWIW, I have never had any problems with ?flush=1 or even ?flush=all and I'm running wamp on my local machine... never more than a few seconds... even on a pretty my old Pentium 4 . I know that's not much help but it does sound like something else is wrong. I don't believe it's necessarily the nature of flush to take ages nor can your machine be simply too slow?

First thanks for your reply. The Server Admin told me that there is no CPU bottleneck. But he noticed that he had to enlarge MySQL Query-Cache and Join-Buffer. I don't now for what it is (I'm not an Admin) but it did not help. He also mentioned that there is a unregular ammount of joins on the site, I think it's on the statistic Pages, but on the Kontakt page there is nothing but a Kontaktform and a Flash-Banner. And even there flush takes ages.

On my local machine I have a Windows with wamp to and there are no Problems.